CBN (Cubic Boron Nitride) is the second hardest substance after diamond. However, it has some advantages over the diamond:
it seems to be a little cheaper to produce
it withstands heat better (1000 degrees Celsius vs. 700 degrees)
it can also dissipate heat better. This means that CBN has an advantage in high-speed grinding machines. When grinding manually, the difference is small. You can grind steel up to 70 HRC with CBN, which should be sufficient for our purposes. For chisels, about 59-63 HRC is common. As with diamond, CBN grinding media is usually purchased as coated plates or grinding wheels.
See therefore also here: